<!DOCTYPE HTML>
<html>
    <head>
        <title>Example</title>
    </head>
    <body>
        <script type="text/javascript">
        
            var myData = {
                name: "Adam",
            };

            document.writeln("Var: " + myData.weather);
            document.writeln("Prop: " + ("weather" in myData));

            myData.weather = "sunny";
            document.writeln("Var: " + myData.weather);
            document.writeln("Prop: " + ("weather" in myData));
            
            myData.weather = null;
            document.writeln("Var: " + myData.weather);            
            document.writeln("Prop: " + ("weather" in myData));

        </script>        
    </body>
</html>
